The present invention relates to a varnishing apparatus, arranged between a printing unit and a delivery unit of a rotary press, or in an independent varnishing machine, for varnishing a printed surface of a paper sheet after printing.
A printed surface of a sheet printed by a rotary press is easily contaminated with ink in the following process since the ink dries slowly. In the case of sheets, offset occurs while they are stacked after a delivery operation. In order to prevent this, a drying device can be arranged midway along a conveying path of the printed sheet or spray powder can be sprayed at this position. However, the drying device makes the entire apparatus bulky. On the other hand, when powder is sprayed, the surface of the sheet is roughened causing it to lose its gloss and this often interferes with the following printing. Alternatively, varnish is coated on the printed surface to prevent it from being contaminated and to put a gloss thereon. This is performed mainly for catalogs, pamphlets, and the like, which must have a good appearance.
The varnishing apparatus of this type is sometimes used as an independent varnishing machine. However, in recent years, due to poor work efficiency caused by, e.g., re-stacking of sheets, the varnishing apparatus is normally arranged midway along a delivery path of a rotary press. A typical varnishing apparatus includes a roller group having a roller arrangement similar to that of a dampening device for supplying dampening water to the surface of a printing plate mounted on a plate cylinder of a rotary press. Varnish contained in a varnish duct is supplied to the surface of a rubber blanket cylinder through the roller group, and the varnish is transferred from the rubber blanket cylinder to a sheet passing between the rubber blanket cylinder and an impression cylinder.
However, the rubber blanket cylinder of varnishing apparatus of this type has a notch on its outer periphery portion and the notch corresponds to that for grippers of the impression cylinder. Therefore, a portion, which corresponds to the notch, of varnish to be transferred from the upstream form roller to the rubber blanket cylinder, cannot be transferred and is left on the peripheral surface of the form roller as a thick varnish film. The thick varnish film is moved to the effective surface of the rubber blanket cylinder upon the next rotation, and is then coated on a sheet. Therefore, the varnish film cannot be uniformly coated on the sheet surface between the gripper end and the sheet end, resulting in irregular density in the circumferential direction of a sheet and degrading a product quality.